Antennas are used in telecommunication applications for radiating or receiving electromagnetic waves, or both. There are multiple kinds of antennas, such as monopole antennas, dipole antennas, inverted F antennas, or split ring resonators (which is also called zeroth order resonator (ZOR)), etc.
FIG. 1 shows a known split ring resonator antenna. The split ring resonator antenna of FIG. 1 comprises an inner ring 7 and an outer ring 3 wherein the inner ring 7 comprises a slit 9 and the outer ring 3 comprises a slit 5. The split ring resonator antenna of FIG. 1 also comprises a slot 15 that can be used for impedance matching and connection to a feeding line 17.
The size of any antenna is proportional to the wavelength λ of the frequency at which the antenna is intended to operate (receive/transmit). There is an optimum size of the antenna where it exhibits its best performance. Decreasing the size of the antenna comes at performance costs most notably the radiation efficiency of the antenna and the usable frequency bandwidth.
Different techniques are known for reducing the size of an antenna while aiming at minimizing the loss in performance. For instance, a mirror image of the half of the antenna can be created by using a groundplane. Another technique is based on optimizing the antenna geometry for example by 3D folding the antenna. However, the techniques used to decrease antenna size are generally frequency sensitive, i.e. will reduce the bandwidth of the antenna and increase resistance losses due to the increased concentration of currents.
“A compact MIMO Antenna using ZOR Split Ring Resonator Radiators with a decoupling Structure” by Seongryong Yoo and Sungtek Kahng discloses a split ring resonator antenna.